The protocol of Montreal for the protection of the ozone layer led to the end of the use of chlorofluorocarbons (CFCs). Less aggressive compounds for the ozone layer, such as the hydrofluorocarbons (HFCs) e.g. HFC-134a replaced chlorofluorocarbons. These latter compounds were indeed shown to provide greenhouse gases. There exists a need for the development of technologies, which present a low ODP (ozone depletion potential) and a low GWP (global warming potential). Although the hydrofluorocarbons (HFCs), which are compounds which do not affect the ozone layer, were identified as interesting candidates, they exhibit a relatively high GWP value. There still exists the need to find compounds which exhibit a low GWP value. Hydrofluoroolefins (HFO) were identified as being possible alternatives with very low ODP and GWP values.
Several processes for production of HFOs compounds, in particular of propenes, were developed. The compound 244bb (2-chloro-1,1,1,2-tetrafluoropropane) is particularly desired as intermediate for the manufacture of 1234yf (2,3,3,3-tetrafluoropropene).
WO2007/079431 describes the synthesis of 244bb from 1233xf (2-chloro-3,3,3-trifluoropropene) either with liquid phase fluorination or gas phase fluorination. Liquid fluorination is disclosed with yields of 87-90%; however only overhead gases are considered, and the liquid phase remaining in the reactor is not analyzed.
US2009/0182179, US2009/0240090, US2009/0312585 and US2010/0036179 disclose the manufacture of 244bb starting from 1233xf. SbCl5 is used as a catalyst in all these references. High selectivities are reported, such as up to 90%. Embodiments such as the addition of HCl in the liquid phase reactor or the use of a mixed catalyst SbCl3/SbCl5 are also disclosed.
WO2009/137658 illustrates the use of 1233xf as raw material for the production of 244bb in liquid phase fluorination. Yield into 244bb is indicated to be between 87 and 89%.
Selectivity is the key factor in the reaction. In fact, low conversion is acceptable if coupled with high selectivity, because it is easier to recycle unreacted feed than disposing by-products and reaction products that find no use in industrial processes, especially chlorinated products.
Thus, there is still a need for a process for the production of compound 244bb with a high selectivity.